SEOUL, Oct 26 (Reuters) - S-Oil Corp, South Korea’s third-largest refiner by capacity, said on Friday that seasonal demand and tight supply in the region are expected to help refining margins increase in the fourth quarter.

“The seasonal demand growth and limited capacity expansions in Asia Pacific will further boost the refining margin,” the refiner, whose top shareholder is Saudi Aramco, said in an earnings statement.

The company also said its new residue fuel oil and olefin plants are expected to begin commercial operations in November. (Reporting By Jane Chung; editing by Richard Pullin)